For wireless mobile applications using a CDMA air interface, a Rake receiver with a simple receiver structure is commonly used. The Rake receiver despreads each multipath component independently and treats other multipaths as noise. Therefore, the Rake receiver suffers performance loss, in particular when the spreading factor is small. In order to achieve better performance, other receiver designs have to be used.
As shown in FIG. 1A, a typical chip-level equalizer 105 may be used to equalize a receiver channel 110 and generate chip samples 115 with suppressed multipath interference for input into a despreader 120, resulting in improved receiver performance. The despreader 120, in FIG. 1A, uses a single spreading code 125. Alternatively, as shown in FIG. 1B, multiple, such as two despreaders 120A, 120B, using respective spreading codes 125A, 125B, may be used in conjunction with the chip-level despreader 105.
The chip-level equalizer 105 may have different implementations, such as using a minimum mean-square error (MMSE) criteria or a zero forcing (ZF) criteria. Since the MMSE equalizer typically performs better than the ZF equalizer, the MMSE equalizer is more commonly used, although ZF equalizers may be used.
It is desirable to provide a high performance wireless receiver, e.g., a CDMA receiver without the drawbacks of the known prior arrangements.